Crunching the Science on Juicing

Crunching the Science on Juicing

Juicing fruits and vegetables was once considered the healthiest of the health trends. Many of us have invested in a juicer, and if we haven't, we probably know friends, family members, or coworkers who have. Those "into" juicing talk about all the fresh vitamins, antioxidants, and enzymes swirling in a richly colored glass of freshly extracted juice. And the health benefits they say they've received are impressive. They talk about the energy they feel, the weight they've lost, or the health conditions that have improved since they started juicing. In fact, I have friends who believe juice brought about "miracle cures" that modern medicine couldn't offer.

I in no way want to discredit the truth that fruits and vegetables are filled with the nutrition we need to help counteract the effects of the Western diet. Meat, eggs, dairy products, and processed foods have all wrought havoc to the finely tuned body we were born with. Add to our poor Western diet a lack of exercise, deficit of sound sleep, inadequate water intake, lack of sunshine and fresh air, plus the environmental toxins of modern life, and it is no wonder that disease is plaguing our society. Research has shown over and over that adding fresh fruits and vegetables to our diet has many advantages for our health, so I applaud anyone who is adding produce to their diet. Fruits and vegetables are important components of a health-optimizing diet, and nearly all Americans need more of them.

The question comes when we stop to consider the ideal way to add fruits and vegetables to our diet. Juicing indeed allows us to consume more produce in a single glass than we could easily eat in one meal. Does this concentration of simple carbohydrates, vitamins, minerals, and antioxidants give juice curative powers? Is there any harm in enjoying our nutrition in a concentrated form not designed by nature? I believe that as we learn about what's lost when we juice our produce, and as we understand the effects that calories separated from fiber have on our system, we might decide that consuming fresh produce in the way nature designed for it to be enjoyed is more in line with our overall health goals.

Fiber is an Integral Part of the Nutrition of Fruits and Vegetables
Nature packages the energy and nutrients in fresh foods with fiber. Fiber plays many important roles in our health:

  • It sweeps out carcinogens and other toxic waste products from our digestive system, helping us avoid colon cancer.
  • It boosts our immune system by fostering the growth of beneficial intestinal bacteria.
  • It soaks up excess estrogen, testosterone, pharmaceutical drugs, and cholesterol, preventing them from entering our bloodstream.
  • It promotes weight loss by helping us feel full at mealtime and keeping us feeling satisfied between meals.
  • It steadies our blood sugar by slowing the absorption of simple sugars into our bloodstream, stabilizing our energy and our moods.
  • It improves gastrointestinal function, protecting us from constipation, diverticulitis, and hemorrhoids.

When we read the nutritional information on a food item, we see a listing for fiber. Fiber is roughage, a type of indigestible carbohydrate that nature synergistically binds with the other nutrients in fruits and vegetables. A juicer uses blades to grind up produce, stripping the fiber from the majority of nutrients in the fruits or vegetables. Of course, not all of the nutrients can be separated from the fiber (often called "pulp"), so we end up tossing out some of the nutrition with the fiber — but lots of nutrients are left in the juice as well. However, along with the vitamins and minerals which remain, all of the calories are also present. After a pass through the juicer, these calories are free from the fiber which would normally cause them to be released slowly. By stripping away fiber, juicing turns carrots and kale into a more processed food, in some ways similar to refined flour. Modifying the fiber is one way in which food is processed.

Not All Fiber is Created Equal
Just as the bran and the germ in wheat carries nutrition that is lost during the refining process, nutrients in the skins of fruits or vegetables are lost when the juicer discards them along with the other fiber. AppleToAppleJuice.w450.webApple skins — with their anti-cancer properties — are an example of fiber we should keep. The journal "Nutrition and Cancer" published a study that showed apple skins battling cancer cells. Researchers blended whole organic gala apples with water and dripped the solution onto breast cancer cells and prostate cancer cells growing in petri dishes. With repeated applications, the cancer cells nearly disappeared. The researchers believe that the cancer cells turn off a protective gene, but that a substance in apple peels turns that gene back on. At the conclusion of the experiment, the researchers suggested that "apple peels should not be discarded from the diet" because apple peel extract "possesses strong antiproliferative effects against cancer cells." If we run our apple through a juicer, we lose the potential benefit of the cancer-fighting properties in apple peel. 

Juicers also discard the polyphenols which are bound tightly to fiber. These amazing phytonutrients play an important role in the prevention and reversal of disease. Many of the benefits of a plant-based diet are attributable to eating polyphenols. When the fiber is removed by the juicing process, the polyphenols are tossed out with it. A study done on grapes showed that 90% of the nutrition is discarded when grapes are juiced. For apples, cranberries, grapes, grapefruit, lemons, and oranges, the antioxidant activity and phytonutrient availability have been shown to be significantly greater in whole fruit as compared to juice. 

Disease Goes Up as Fiber Comes Down
Without fiber, juice becomes a caloric bomb. The calories in juice quickly absorb straight through the intestinal wall and burst into the bloodstream, giving us a "rush" of energy. The explosion of sugar spikes the blood glucose level, triggering a deluge of insulin from the pancreas to flood out to the rescue in an attempt to drive down the glucose level. This insulin spike causes two problems. First, juice-induced sugar spikes may overwork our pancreas, pushing that insulin-producing gland towards prediabetes. According to the conclusion of a study published in 2013 in The BMJ, "Greater consumption of specific whole fruits, particularly blueberries, grapes, and apples, is significantly associated with a lower risk of type 2 diabetes, whereas greater consumption of fruit juice is associated with a higher risk." 

The second problem caused by high levels of insulin in the blood is an increased risk of cancer due to insulin-like growth factor 1 (IGF-1) which is an anabolic hormone produced primarily in the liver. When the liver detects increased insulin in the bloodstream, it is stimulated to produce IGF-1. Under normal conditions, this is a positive thing. IGF-1 is a growth promoter. During our time in the womb and continuing throughout childhood, IGF-1 production is vital to our growth and development. Even into adulthood, the anabolic (body-building) effects of IGF-1 are beneficial, helping us maintain our body's many cells or build muscle mass when we exercise. But IGF-1 presents a paradox. Although it is necessary for proper growth, development, and maintenance of the human body, elevated levels of IGF-1 in adulthood promote both the aging process and the growth of cancerous tumors

The levels of IGF-1 circulating through our bloodstream are affected by what we eat. The Western diet of animal products and processed foods is excessively high in protein and in refined carbohydrates, both of which stimulate the production of IGF-1. But "bad" foods aren't the only ones that stimulate IGF-1 production. Any refined carbs — like the ones that remain in juice once the fiber is stripped away — cause a spike in blood glucose, sending insulin flooding out of the pancreas. This in turn stimulates IGF-1 production and at the same time decreases production of IGF-binding proteins which mitigate the effects of IGF-1. Elevated insulin and its accompanying high IGF-1 levels may help explain why there is an increased incidence of breast, colon, and pancreatic cancer associated with type 2 diabetes.

Plant Enzymes Offer More Nutritional Benefit Than Digestive Benefit
Raw fruits and vegetables carry many benefits for our health. For one, fruits and veggies have the best ratio of calorie density to nutrition of any food. OrangeAppleStrawberryToJuice.w450.webWe can eat lots of produce, feel comfortably full, max out on micro nutrients, and still have not have ingested excess calories. I encourage my patients to eat plenty of fruits and veggies, and if they enjoy some of them raw, I say, "Go for it." In fact, due to the enzyme action that takes place within the plant when chewing or chopping breaks the cell walls, both broccoli and garlic have enhanced nutritional properties when they're eaten raw. So, it's a good idea to occasionally enjoy these veggies uncooked. When it comes to juicing though, some people believe that the enzymes contained in raw juice assist our digestion. Raw foodists talk about uncooked foods as "live" and cooked foods as "dead." It is true that the heat of cooking denatures some of the enzymes in produce. This is not, however, a true problem for our digestive system.

Proponents of raw food sometimes claim that the human body needs plant enzymes to replace its own dwindling supply of digestive enzymes. This is based on a faulty understanding of enzyme production. Our body does not run out of enzymes. Michael Greger, MD, points out, "Our body makes all the enzymes we need to function from the protein we eat." Joel Fuhrman, MD, concurs.  He says, "Every living cell makes enzymes for its own activities. Human cells are no exception." Enzymes are a type of protein molecule which our body is designed to manufacture. From cradle to grave, we build digestive enzymes from the amino acids in our diet.

The second misunderstanding is that we need the help of plant enzymes in fresh juice to augment our digestive enzymes. Although plant enzymes may initially remain alive and active, they will ultimately not survive the acid bath of our digestive juices. "After they are ingested, the enzymes contained in plants do not function as enhancements or replacements for human digestive enzymes. These molecules exist to serve the plant’s purpose, not ours," explains Dr. Fuhrman. This is not to say that plant enzymes are of no value. "Many plant enzymes function as phytochemical nutrients in our body and can be useful to maximize health," he continues. When we consume fresh produce, "the plant enzymes get digested by our own digestive juices along with the rest of the food and are absorbed and utilized as nutrients." So, plant enzymes are indeed beneficial, but the concept of easing our digestion by drinking fresh juice is not entirely accurate.

In fact, drinking produce rather than chewing it may effectively limit the natural enzyme action which we need in order to gain the maximum nutrition from our food. Our bodies were designed for the first step of digestion to take place in the mouth. Saliva contains the enzyme amylase which begins breaking starch down into simpler sugars. When we drink our produce rather than chew it, our saliva may not have the opportunity to interact with the food we are quickly swallowing. Ultimately, juice's value is in the amount of nutrition our body absorbs; skipping the step of chewing may limit juice's interaction with the digestive enzyme in our saliva.

Swirling Controversy on Green Juices
Green juice is hailed as an elixir by many juicing proponents. Pounding back a box of greens in one gulp sounds like a healthy idea, doesn't it? BellPeperTomatoBrocolliToJuice.w450.webCaldwell Esselstyn, Jr., MD, author of Prevent and Reverse Heart Disease, doesn't think so. Dr. Esselstyn advocates consuming up to six servings a day of green, leafy vegetables in order to provide the nitric oxide our bodies lack after we've damaged the delicate lining of our blood vessels with a diet of processed foods, oil, and animal products. As we chew, Dr. Esselstyn explains, the nitrates in greens mix with the friendly bacteria in the mouth and are thereby reduced to nitrites which further reduce to nitric oxide as they hit the gastric juices of our stomach. The nitric oxide is absorbed and aids our cardiovascular system, allowing blood to flow smoothly through the vessels and helping the vessels expand to accommodate the changing needs for blood volume. Any nitrites not converted to nitric oxide are reabsorbed into the system and returned to the mouth through the saliva to go through the process again, keeping the body supplied with life-enhancing nitric oxide. Drinking our greens in the form or juice or smoothies, Dr. Esselstyn says, skips the vital step of chewing, preventing the conversion of nitrates to nitrites.

Like Dr. Esselstyn, Dr. Greger is a big fan of greens. However, he believes that the nitrate to nitrite conversion will still take place even if we drink our greens in juice. According to Dr. Greger, the body will still make use of the nitrates, but there will be a delay. He says the nitrates that are swallowed in the green beverage will eventually be returned to the mouth through the saliva and can then convert to nitrites and eventually to nitric oxide.

In either case, both doctors know that many people sweeten their green drink with fruit juice, filling it with fructose. The resulting green drink actually damages the endothelial cells with the concentrated natural sugar, says Dr. Esselstyn. On the other hand, green juices by themselves tend to be sour which poses the problem of eroding tooth enamel, says Dr. Greger. So, what's the verdict on green juices? It seems to me that both of my colleagues would agree that chewing whole, intact greens will give us the necessary nitrates, will not damage our endothelial cells with concentrated sugar, and will not bathe our teeth in excess acid. 

Fruit Can Make Juice Sweetly (Un)Satisfying
A glass of fruit juice usually contains multiple pieces of fruit. Eight ounces of apple juice contains up to 6 apples, while a cup of orange juice is made from four to five medium oranges. Jeff Novick, MS, RD, compares fruit juice to soda, showing that ounce for ounce, fruit juice can have more sugar and calories than a soft drink. TomatoesToJuice.w450.webDrs. Barry Popkin and George Bray are the researchers who in 2004 called out high fructose corn syrup in soft drinks for its damaging effect on health. Now, they are blowing the whistle on the trend toward juices and smoothies. Dr. Popkin says that "in every country they've been replacing soft drinks with fruit juice and smoothies as the new healthy beverage. So you will find that Coke and Pepsi have bought dozens [of fruit juice companies] around the globe." In their 2013 review article, the researchers state, "Fructose [which is the sugar in fruit] remains a major component of our global diet. To date, to the best of our knowledge every added amount of fructose-–be it from fruit juice, sugar-sweetened beverages or any other beverage or even from foods with high sugar content–-adds equally to our health concerns linked with this food component."

Knowing that excess sugar intake raises blood pressure and that juice is a concentrated source of natural sugar, scientists wondered if fructose would affect blood pressure in a similar manner. The results of a 2015 study indicated that central systolic blood pressure was 3–4 mmHg higher for those who consumed fruit juice daily compared to those who consumed it rarely or occasionally. 

Fruit juice also has a negative effect on triglycerides. When test subjects with elevated triglycerides were fed a diet rich in sugar for 6 weeks, their levels increased by 45.2%. It does not seem to matter to our bodies that fructose is a "natural" sugar. In a study published in 2010, fructose was shown to cause a greater rise in triglycerides in men than did glucose. For those struggling with obesity, a 2009 investigation found that beverages high in fructose may further exacerbate their adverse metabolic condition by lowering insulin secretion and raising triglycerides. And a 2004 study found that dietary fructose increased triglycerides in women while having a negative effect on satiety (the feeling of fullness).

Like all sugary substances, sweet juices are addictive. Our bodies instinctively know when we eat something concentrated in calories. A signal goes off in the pleasure center of our brain, and suddenly we find ourselves craving more of the calorie-dense food. Because we mistakenly think of juice as a "natural" food rather than as the processed food that it really is, we may easily give in to the desire for more. The result is more weight, not just for us, but for our children who regularly drink fruit juice. A 2007 German study found the body mass index (BMI) of teenage girls increases more with fruit juice than with soft drinks — although both beverages caused weight gain. A study published in the journal "Pediatrics" in 2006 showed that overweight children and children at risk for becoming overweight increased their adiposity gain when they drank fruit juice but reduced their adiposity gain when given whole fruits instead. 

Researchers Are Examining the Claims for Exotic Juices
Exotic fruits present a new area for research. The juices of these usually tropical fruits are bottled and sold at health food stores across the country. Since we rarely have the opportunity to eat these fruits in their whole form, is it beneficial to get the nutrients we can from their juice? John McDougall, MD, points out that the promising preliminary studies done on juices like noni, mangosteen, acai, and goji berries were conducted on cells cultured in the laboratory, not done on living people. Currently, no definitive data recommends these juices, and in the case of mangosteen, there seems to already be some indication that it is not the "super juice" it was initially thought to be. Until more thorough studies have been completed, there doesn't seem to be sufficient documented benefit to justify the cost of these exotic juices. If you do choose to use them, please read the labels. Sometimes these expensive bottled juices are actually mixtures of exotic juice and juice from more common fruits and may contain very little of the exotic juice advertised on the label. 

Does Juicing Weigh Us Down or Help Us Lighten Up?
Many people have found juicing helpful in their quest to shed excess pounds. Joe Cross' documentary "Fat, Sick, and Nearly Dead" demonstrates that juicing can be effective for weight loss. But Joe's success isn't shared by everyone who processes their produce through a juicer. The internet has many articles and first-person accounts of individuals who have started juicing and actually gained weight. So what could be happening? Do different body types require different weight loss methods? No, the answer lies more in what is being juiced and the place juice is taking in the overall diet. Juicing for weight loss may work if the juice is replacing meals, as happened in Joe's case. In his story, Joe admitted that he was accustomed to eating entire pizzas at a single meal. Replacing a diet heavy in animal foods and fat-laden fast food with fresh vegetable juice of course did "miraculous" things for his health. I applaud his success and his efforts to help others recover their health through fresh fruits and vegetables. Joe's health reversal was due not only to the robust nutrition of fresh plant foods, but also to the low-calorie nature of his liquid diet. If, however, we are drinking juice, and we are continuing to eat our usual meals, we may find our weight going up, not down. While a glass of juice has considerably fewer calories than a large pizza, it still contains enough calories to cause us to gain weight if we are adding those calories to an already energy-sufficient diet. apple refinningoptiThere was a fascinating study published in 2009 showing what happens when we drink juice before a meal. At each test meal, subjects were given apples in different forms, then served an all-they-could-eat pasta meal. The first test meal started with skinless apple slices; the next one applesauce; then apple juice with fiber followed by apple juice without fiber. The apple portions given were carefully controlled across the various forms to be as equal as possible in weight, energy content, energy density, and ingestion rate — only the fiber content differed. On different days, test subjects were given one of the apple appetizers, then asked to rate their sense of satiety (feeling full and satisfied). After a short waiting period, subjects were offered the pasta, and the quantity they ate was measured. The results? Subjects ate 91 fewer calories when eating apple slices than when eating applesauce. When they had either of the juices before the meal, they ate over 150 calories more as compared to their intake after the sliced apple. In other words, the apple slices filled them up more, so they ate less cheese tortellini and sauce. The take away message is that processing produce makes it less filling and satisfying. Generally, when we don't feel full, we will eat until we do. That is why adding the calories of freshly juiced produce to our current diet can cause weight gain.

Weight loss can also be sabotaged if our juice is high in natural sugars — such as the sugar in fruits, carrots, or beets. Natural sugars raise our insulin level. Insulin leads us to store body fat in places where we'd prefer body fat not to accumulate, like our belly. Not only that, but when insulin surges, hunger follows. After a few big gulps of insulin-triggering juice, we may soon find ourselves fighting food cravings as our blood sugar spikes and then dives to new lows.

Detoxing with Fresh Fruits and Vegetables
Some advocate using the juice of fresh fruits and vegetables to detoxify the organs of elimination, specifically the liver, kidneys, and colon. There is no doubt that a Western diet and modern lifestyle have introduced toxins into our bodies; juice fasting may be one method to help clear those out of the system. However, I recommend that my patients adopt a detox lifestyle which is a more natural way to cleanse their bodies of accumulated toxins. We have organs of elimination because the human body was designed to eliminate toxins, just as it was designed to extract nutrients from our food or designed to defend itself from the threat of germs. We need to live and eat in such a way as to support our body's design. If we want to cleanse our body, we must first do what we can to remove toxins from our environment. For our diet, that means eliminating toxic substances like animal products and processed foods. Next, we need to eat to support constant cleansing. Eating fruit, vegetables, beans, whole grains, nuts and seeds (with no added oil) gives our organs of elimination the fiber and nutrients necessary to help the body shed toxins. Plenty of pure water — at least 64 ounces a day, fresh air, and exercise are all vital elements of a healing and cleansing lifestyle. This is a gentle and sustainable method to detox.

Juice is Best When it Crunches
There is no question that fruits and vegetables pack a power punch of nutrients that helps our body perform at its highest potential. Fiber is one of the nutrients essential to our optimal health. That's why I maintain that despite the benefits of juice, fruits and veggies are still best when they crunch. Whether it happens in a large factory or in our own kitchens, any time the fiber is stripped out of produce, our food has become more processed. Processed food lacks important nutrients, jolts our system with a rush of sugar, and may bring on the unintended consequences of disease and obesity.

Fiber is nature's answer to these problems. That's why I like my juice crunchy. Bite into an apple. Nibble a nectarine. Chew up a carrot, or chomp a green salad. You'll get all the benefits of juice with no loss of fiber, no depletion of nutrients, no overload of sugar, lower risk of disease, plus all the flavor nature packaged into the goodness of plants.

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  1. Randy Clark

What about "blending"? Nothing is wasted like in the pulp removal of a juicer. There's no firing or blanching or bleaching going on, no "refining" that would make it remotely "processed". If you get too anal with things, you would be reduced to not eating at all, as your body processes food, so anything you put in your mouth would be "processed".

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  1. Linda Carney MD

Thank you Randy Clark for your comment.

You are correct that blending is different from juicing in that the fiber is not removed.

Blending does, however, modify the fiber quite a bit, which increases the rate of absorption of carbohydrates into the bloodstream. This fast absorption can cause spikes in the level of blood glucose, which may have a detrimental effect on insulin levels.

For...

Thank you Randy Clark for your comment.

You are correct that blending is different from juicing in that the fiber is not removed.

Blending does, however, modify the fiber quite a bit, which increases the rate of absorption of carbohydrates into the bloodstream. This fast absorption can cause spikes in the level of blood glucose, which may have a detrimental effect on insulin levels.

For a good read on this subject I would like to suggest you read the following article:
Blending Up the Smoothie Controversy: https://www.drcarney.com/articles/entry/blending-up-the-smoothie-controversy

as well as our article entitled:
Food Processing Made Simple: https://www.drcarney.com/articles/entry/food-processing-made-simple

After you have read these articles if you still have questions we would love to receive them in our discussion forum at https://www.drcarney.com/talk

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  1. Ken Thomas

I think the point is to minimize processing before it passes one's lips. Personally, I much prefer eating my food as opposed to drinking it. I get to savor the taste longer with chewing.

As far as the processing thing goes, I understand that having it juiced, blended or pre-chewed hits the blood-stream with a rush (no chewing time between swallows), prompting overdose counteractive responses.
...

I think the point is to minimize processing before it passes one's lips. Personally, I much prefer eating my food as opposed to drinking it. I get to savor the taste longer with chewing.

As far as the processing thing goes, I understand that having it juiced, blended or pre-chewed hits the blood-stream with a rush (no chewing time between swallows), prompting overdose counteractive responses.

I believe that "anal" is an "eye of the beholder thing". As a Type-1 diabetic, many think I am obsessively anal about blood-sugar control, but my "anal-ness" seems perfectly natural to me.

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  1. Sean Carney

Thanks Ken for your well balanced perspective.

And, of course thank you Dr. Carney for replying. :-)

And Randy your comment is appreciated although the "too anal" part could probably have been left out and the idea would have still come across just fine. :-)

Again, thanks for joining us. Feel free to become a member and post questions in the forum.

Sean

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  1. Ken Thomas

Oops! Forgot to mention one of the important purposes of chewing - Saliva. Human saliva contains important digestive components that get integrated with the food during the chewing process. Without chewing, that part of the digestive process is missing. Note: The saliva of all herbivores contain digestive components - carnivore's do not.

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  1. Sean Carney    Ken Thomas

Good point for sure. We have another article that goes into that subject quite a bit called "Chew Chew Training for Improved Digestion"

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